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Law of Definite Proportions

Law of Definite Proportions. Clues to an invisible world. What is an element?. A substance which can’t be separated or divided into a different substance by normal chemical means. Each has characteristic properties. Humans have been learning about the elements for a long time.

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Law of Definite Proportions

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  1. Law of Definite Proportions Clues to an invisible world

  2. What is an element? A substance which can’t be separated or divided into a different substance by normal chemical means. Each has characteristic properties. Humans have been learning about the elements for a long time.

  3. Famous guys in the history of chemistry Hammurabi – 1700 BC Babylonian king wrote of metals and heavenly bodies (but was most famous for his “code” of laws) Democritus – 450 BC Ancient Greek said atoms are the simplest form of matter Aristotle -- 300 BC Ancient Greek philosopher wrote of 4 elements—earth, fire, water, air. (Did not believe in atoms)

  4. Famous guys in the history of chemistry, continued In the early 1800s, chemists began to combine elements to form new substances; they especially noted the quantities of elements combining together. Dalton observed: 8 lbs Oxygen combined with 1 lb Hydrogen 9 lbs water 5 lbs Nitrogen combined with 1 lb Hydrogen 6 lbs Ammonia He concluded that elements combined in mass ratios.

  5. Famous guys in the history of chemistry, continued Gay-Lussac observed that: Hydrogen combined with Oxygen in a ratio of 2:1 by VOLUME  to form Water (now known as H2O) Nitrogen and Oxygen combined in a ratio of 1:1 by VOLUME to form Nitrous Oxide (NO, used in anesthesia) He concluded that elements combine in volume ratios

  6. Famous guys in the history of chemistry, continued Joseph Proust – 100 lbs of copper combined with acid and carbonates always yielded 180 pounds of green carbonate. In 1799 he proposed the Law of Definite Proportions:elements combine in definite ratios when forming compounds He also proved that grape sugar is the same as the sugar in honey.

  7. Test yourself • The first guy to come up with the idea of atoms was: A) Aristotle B) John Dalton C) Democritus D) Joseph Proust C) Democritus

  8. Test yourself 2. The first guy to notice elements combining in ratios by mass was: A) Aristotle B) John Dalton C) Democritus D) Joseph Proust John Dalton He noticed that 9 pounds of water was made of 8 pounds of oxygen and 1 pound of hydrogen

  9. Test yourself 3. The first guy to notice elements combined in ratios by volume was: A) Aristotle B) John Dalton C) Democritus D) Gay-Lussac Gay-Lussac He noticed that hydrogen and oxygen always combined in a ratio of 2:1by volume to make water

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